The disclosure of Japanese Patent Application No. 2002-163576 filed on Apr. 26, 2002, including the specification, drawings and abstract are incorporated herein by reference in its entirety.
1. Field of Invention
The invention relates to an evaporative fuel processing system for an in-cylinder fuel injection type internal combustion engine, in which an evaporative fuel processing mechanism is provided for purging the evaporative fuel in a fuel supply system to an intake system and an evaporative fuel processing method. More specifically, the invention relates to an evaporative fuel processing system and method for controlling a flow rate of the evaporative fuel to be purged to the intake system by the evaporative fuel processing mechanism in accordance with an air/fuel ratio of the internal combustion engine.
2. Description of Related Art
Generally in an internal combustion engine, an evaporative fuel generated in a fuel supply system such as a fuel tank is temporarily adsorbed in a canister. The adsorbed evaporative fuel is introduced as purge gas to the intake system at a predeternined timing so as to be treated or purged. As the purge gas has a high fuel content, the air/fuel ratio may fluctuate if the quantity of the purge gas is not appropriately controlled.
In JP-A 2001-152931, a variance tendency of an actual air/fuel ratio with respect to a target air/fuel ratio, which is obtained by an air/fuel ratio feedback control is monitored so as to learn the fuel concentration of the purge gas (purge concentration) on the basis of the monitored variance tendency. The flow rate of the purge gas is controlled in accordance with the purge concentration such that appropriate quantity of the purge gas in accordance with the operating state of the engine is introduced into the intake system.
The internal combustion engine is provided with a crankcase emission control system for treating gas that leaks out of the cylinder to the crankcase, that is, blowby gas having strong acidity that may cause rust on a metal part of the engine body or deteriorate the lubricating oil therein. The crankcase emission control system introduces new air from outside (through air cleaner provided in the intake system) into the engine body, and circulates the introduced air within the crankcase so as to be returned to the intake system. Implementing the aforementioned scavenging process makes it possible to treat the blowby gas without being discharged to the outside.
Returning the blowby gas containing uncombusted fuel to the intake system may substantially fluctuate the fuel injection quantity. Normally, however, the uncombusted fuel concentration of the blowby gas is not so high nor largely fluctuates. Therefore, an air/fuel ratio feedback control is performed to cope with the fluctuation of the fuel injection quantity so as to restrain the adverse effect resulting from such fluctuation.
Unlike the internal combustion engine using the intake port, in the in-cylinder fuel injection type internal combustion engine where the fuel is directly injected into the cylinder from the fuel injection valve, the distance between the nozzle hole of the fuel injection valve and the inner peripheral surface of the cylinder is so short that the injected fuel directly impinges on the inner peripheral surface. The aforementioned type of the internal combustion engine may cause problems as described below.
In the above type of the internal combustion engine in the cold state, it is difficult to promote atomization of the fuel in the cylinder, and as a result, the injected fuel is partially kept uncombusted and adhered to the inner peripheral surface of the cylinder. The adhered fuel is mixed with the lubricating oil applied on the inner peripheral surface of the cylinder for lubrication. Accordingly, the lubricating oil is diluted with the fuel.
The lubricating oil that has been diluted with the fuel is peeled off from the inner peripheral surface of the cylinder as the piston reciprocates, and returned to a crankcase (more particularly, an oil pan formed in the crankcase) so as to be used for lubricating the piston and the like in the internal combustion engine. If the aforementioned dilution of the lubricating oil frequently occurs, the quantity of the fuel to be mixed with the lubricating oil in the crankcase, that is, the whole lubricating oil supplied for lubricating the internal combustion engine may gradually increase.
As the fuel content in the lubricating oil increases, a large quantity of the fuel evaporates from the lubricating oil. This may considerably raise the fuel concentration in the blowby gas. If the aforementioned blowby gas with increased fuel concentration is introduced in the intake system, the variance tendency of the actual air/fuel ratio with respect to the target air/fuel ratio largely fluctuates. If the purge concentration is learned in the aforementioned case, however, it may be mistakenly determined that the fluctuation of the air/fuel ratio variance tendency has been caused by the change in the purge concentration.
The adverse effect resulting from the aforementioned error in learning of the purge concentration is more likely to occur in the engine operation at low load where the flow rate of the purge gas is set to a small value. Therefore, if the engine operation is rapidly brought into the transient stage from the low load where it is likely to be adversely affected by the error in the learning to the high load where it is less likely to be adversely affected by the error, the purge concentration varies as if it were caused by the change in the load state. As a result, fluctuation of the air/fuel ratio during such transient operation of the engine inevitably occurs.
It is an object of the invention to provide an evaporative fuel processing system for an in-cylinder fuel injection type internal combustion engine to restrain fluctuation of the air/fuel ratio of the engine at the transient operation stage, which is caused by an adverse influence of dilution of the lubricating oil with fuel to purging control, especially, the error in learning of the purge concentration.
According to an embodiment of the invention, an evaporative fuel processing system for an in-cylinder injection type internal combustion engine includes an evaporative fuel processing mechanism that includes a canister to which an evaporative fuel in a fuel supply system is adsorbed and performs an operation for purging the adsorbed evaporative fuel into an intake system of the internal combustion engine. The system further includes a controller that estimates a degree of dilution occurred in a lubricating oil for the internal combustion engine with a fuel mixed therewith, and inhibits the purging operation performed by the evaporative fuel processing mechanism when the estimated degree of dilution is equal to or larger than a predetermined value.
In the aforementioned embodiment, the degree of dilution of the lubricating oil with the fuel is estimated. The purging performed by the evaporative fuel processing mechanism is inhibited if the estimated degree of dilution is higher than a predetermined level. This makes it possible to prevent the error in learning of purge concentration even if the fuel evaporating from the lubricating oil is introduced into the intake system. This may restrain fluctuation of the air/fuel ratio of the engine at the transient operation stage, which is caused by the adverse influence of the dilution of the lubricating oil with the fuel to the purge control, especially, the error in learning of the purge concentration.
In the case where quantity of the evaporative fuel from the lubricating oil is increasing, it is likely that the actual air/fuel ratio shows a variance tendency from the target air/fuel ratio to the fuel rich side. Meanwhile, it is unlikely that the actual air/fuel ratio shows a variance tendency from the target air/fuel ratio to the fuel lean state. Even if an air/fuel ratio correction amount derived from the aforementioned variance tendency is increasing (the variance from the reference value of the air/fuel correction amount is large), the air/fuel correction amount is increased to compensate the air/fuel ratio to the fuel rich side so far as it is caused by the increasing quantity of the evaporative fuel from the lubricating oil. Conversely, in the case where the air/fuel ratio correction amount is increasing to compensate the air/fuel ratio to the fuel lean state, such increase in the correction amount is considered to be caused by the reason other than the increase in the evaporative fuel quantity.
According to the embodiment of the invention, the controller inhibits the purging operation when the estimated degree of dilution is equal to or larger than the predetermined value, and an air/fuel ratio correction amount of an air/fuel ratio feedback control obtained in accordance with a variance tendency of an actual air/fuel ratio with respect to a target air/fuel ratio increases by a predetermined amount or more so as to compensate the actual air/fuel ratio to a fuel rich side with respect to the target air/fuel ratio.
In the aforementioned embodiment, performance of purging is inhibited if the estimated degree of dilution is higher than the predetermined level, and the air/fuel ratio correction amount is increasing by a predetermined amount so as to compensate the air/fuel ratio to the fuel rich side. When the evaporative fuel quantity is increased by the dilution of the lubricating oil, and the resultant air/fuel ratio variance occurs, performance of purging is inhibited. In the state where the estimated degree of dilution is higher than the predetermined level and the air/fuel ratio correction amount shows the value to compensate the air/fuel ratio to the fuel lean state, performance of purging is not inhibited. That is, even if the degree of dilution is in relatively high level, performance of purging is not inhibited so far as it is determined that no learning error occurs. This makes it possible to avoid unnecessary inhibition of performance of purging.
According to the embodiment of the invention, the controller estimates the degree of dilution on the basis of a historical record of an operation of the internal combustion engine. The degree of dilution of the lubricating oil varies with the historical record of operation of the internal combustion engine. For example, if the cold short-trip is repeatedly performed, that is, the cycle in which the internal combustion engine is started at a low temperature of the engine, and stopped before the engine temperature sufficiently rises up is repeatedly implemented, the degree of dilution of the lubricating oil with the fuel greatly increases. Meanwhile, if the internal combustion engine is continuously operated for an extended period of time even after completion of the warming-up, the degree of dilution decreases as the fuel contained in the lubricating oil gradually evaporates. As a result, the degree of dilution of the lubricating oil may be estimated by referring to the historical record of the operation of the internal combustion engine.
More specifically, the controller monitors the operation of the internal combustion engine in a state where the degree of dilution is increasing and estimates the degree of dilution on the basis of a result of monitoring the operation. Therefore the degree of dilution may be accurately estimated under the condition where it is increasing.
When the temperature of the engine at start-up is high, it is not likely that the fuel adheres to the inner peripheral surface of the cylinder. Accordingly, no increase in the degree of dilution of the lubricating oil with the fuel occurs. It is possible to determine that the internal combustion engine is operated under the condition where the degree of dilution is increasing if the temperature of the engine at start-up that has been monitored is equal to or lower than a predetermined temperature.
Even when the temperature of the engine at the start-up is relatively low, adhesion of the fuel to the inner peripheral surface of the cylinder may be restrained by continuously operating the internal combustion engine for an extended period of time. As the combustion heat generated in the cylinder increases the temperature of the lubricating oil, quantity of the evaporative fuel from the lubricating oil increases.
In the case where the time elapsing from the start to stop of the internal combustion engine becomes long, the degree of dilution may temporarily increase owing to dilution at the earlier operation stage of the engine, but gradually decrease thereafter as the fuel evaporates from the lubricating oil during subsequent operation of the engine continuously. Such decrease in the degree of dilution may offset or exceeds the increase in the degree of dilution generated at the earlier operation stage of the engine. Therefore the historical record of the engine operation under the condition where the degree of dilution is increasing is no longer necessary.
In the aforementioned embodiment, the time elapsing from start to stop of the engine is measured. It is possible to determine that the internal combustion engine has been operated under the condition where the degree of dilution is increasing if the engine temperature at start-up is equal to or lower than the predetermined temperature, and the measured time is equal to or shorter than the predetermined value.
If larger quantity of the fuel is supplied for combustion in the engine within a predetermined time elapsing from start to stop of the engine, the temperature within the cylinder increases at an earlier stage. This makes it possible to restrain adhesion of the fuel to the inner peripheral surface of the cylinder at the earlier stage, and to further promote evaporation of the fuel at the increasing temperature of the lubricating oil. The rate of increase in the cylinder temperature or the lubricating oil temperature as aforementioned has a correlation with the total amount of combustion heat generated within the cylinder after start-up of the engine. Therefore it is preferable to monitor the total amount of combustion heat generated within the cylinder for the time from start to stop of the engine so as to accurately determine whether the internal combustion engine has been operated at the increasing degree of dilution.
In the aforementioned embodiment, the controller estimates a total quantity of combustion heat generated in a cylinder from start to stop of the internal combustion engine on the basis thereof, and determines that the internal combustion engine is operated in the state where the degree of dilution is increasing when a temperature of the engine at the start is equal to or lower than a predetermined temperature, and the estimated total quantity of the combustion heat is equal to or smaller than a predetermined quantity.
The aforementioned embodiment further makes it possible to determine that the internal combustion engine has been operated under the condition where the degree of dilution is increasing. Accordingly, the increase in the degree of dilution can be accurately estimated. It is preferable to directly detect a temperature within the cylinder as the engine temperature, for example. However, the temperature of the cooling water, intake air temperature, outside temperature or any combination thereof may be used to estimate the engine temperature.
In the aforementioned embodiment, it is accurately determined that the internal combustion engine has been operated under the condition where the degree of dilution is increasing if the engine temperature at start-up is equal to or lower than the predetermined temperature, and the total amount of combustion heat is equal to or less than the predetermined value. The predetermined value with which the total amount of combustion heat is compared may be set to be variable in accordance with the engine temperature at start-up. When the engine temperature at start-up is equal to or lower than the predetermined temperature but measures relatively higher, the increase in the degree of dilution at the earlier operation stage of the engine is reduced. Therefore the total amount of combustion heat required to offset or exceed the increase in the degree of dilution may be reduced. It is preferable to set the predetermined value with which the total amount of combustion heat is compared to be a smaller value as the engine temperature at start-up becomes higher. The aforementioned structure is effective for making the determination whether the internal combustion engine has been operated under the condition where the degree of dilution is increasing.
According to the embodiment, the controller determines that the total quantity of the combustion heat is equal to or smaller than the predetermined quantity when one of a sum of intake air quantity and a sum of fuel injection quantity obtained from the start to stop of the internal combustion engine is equal to or smaller than a predetermined value. The amount of combustion heat within the cylinder resulting from the fuel injection varies with the air/fuel ratio or the injection timing at the fuel injection as well as the intake air quantity, fuel injection quantity and the like. Therefore it is effective to calculate the total amount of combustion heat using the intake air quantity or the fuel injection quantity having a weighting on the basis of the air/fuel ratio or the ignition timing such that the amount of combustion heat is accurately estimated.
According to the aforementioned embodiment, the controller determines whether the degree of dilution is increasing on the basis of one of a lubricating oil temperature and a parameter correlating therewith, and estimates the degree of dilution on the basis of a counter value which is increased when it is determined that the internal combustion engine is operated in the state where the degree of dilution is increasing, and gradually decreased when it is determined that the internal combustion engine is operated in the state where the degree of dilution is decreasing.
As described above, the degree of dilution gradually increases as the cold short-trip, that is, engine operation at the increasing degree of dilution is repeatedly performed. Meanwhile, when the internal combustion engine has been operated for an extended period of time and the lubricating oil temperature increases, quantity of the evaporative fuel contained in the lubricating oil increases. Accordingly the degree of dilution gradually decreases as the elapse of time.
In the aforementioned embodiment, the counter value is set to be variable in accordance with the increase or decrease in the degree of dilution. This makes it possible to estimate the degree of dilution further accurately on the basis of the counter value.
According to the embodiment of the invention, the controller calculates a rate of increase in the degree of dilution on the basis of a parameter correlating with quantity of the fuel adhered to an inner peripheral surface of a cylinder of the internal combustion engine during fuel injection; and estimates the degree of dilution so as to be updated on the basis of the calculated rate of increase.
The degree of dilution gradually increases as the lubricating oil applied on the inner peripheral surface of the cylinder is diluted with the fuel adhered thereto through fuel injection, and the diluted lubricating oil is mixed with the remaining lubricating oil. It is possible to calculate the rate of increase in the degree of dilution, that is, how far the dilution proceeds, on the basis of the quantity of the fuel adhered to the inner peripheral surface of the cylinder during fuel injection (more specifically, the parameter relating thereto).
Accordingly, the current value of the degree of dilution may be updated on the basis of the resultant rate of increase as described above so as to be set to a newly learned value. This makes it possible to accurately estimate the degree of dilution.
It is difficult to directly detect the quantity of the fuel adhered to the inner peripheral surface of the cylinder. In this embodiment, the controller calculates the rate of increase in the degree of dilution using a parameter correlating with the quantity of the fuel adhered to the inner peripheral surface of the cylinder, which includes at least one of fuel injection quantity, fuel injection timing, and a temperature of the internal combustion engine. The quantity of the fuel adhered to the inner peripheral surface tends to increase in the following conditions where:
(a) the fuel injection quantity is large;
(b) the fuel injection timing is set at a timing when the piston is located closer to the bottom dead center side; and
(c) the engine temperature is relatively low.
The quantity of fuel adhered to the inner peripheral surface may be obtained considering the above-described conditions.
According to the embodiment, the controller further estimates quantity of the fuel evaporating from the lubricating oil on the basis of one of a lubricating oil temperature and a parameter correlating therewith, calculates a rate of decrease in the degree of dilution on the basis of the estimated quantity of the fuel, and learns the degree of dilution so as to be updated on the basis of the calculated rates of increase and decrease.
The dilution of the lubricating oil gradually becomes extinct as the lubricating oil temperature rises up in the engine combustion heat and the like, and the fuel contained in the lubricating oil evaporates as the lubricating oil temperature rises. It is, thus, possible to calculate the rate of decrease in the degree of dilution, that is, how far the dilution gets extinct on the basis of the lubricating oil temperature or the parameter correlating therewith.
In the aforementioned embodiment, the current value of the degree of dilution is updated on the basis of not only the rate of increase in the degree of dilution but also the rate of decrease in the degree of dilution so as to be set to a newly learned value. As a result, the degree of dilution can further be accurately estimated on the basis of the rates of both increase and decrease in the degree of dilution.
According to an embodiment, an evaporative fuel processing system for an in-cylinder injection type internal combustion engine includes an evaporative fuel processing mechanism that includes a canister to which an evaporative fuel in a fuel supply system is adsorbed and performs an operation of purging of the adsorbed evaporative fuel into an intake system of the internal combustion engine. The system further includes a controller that obtains a plurality of air/fuel ratio learned values corresponding to a plurality of engine load regions, each of which is used for compensating a variance tendency of an actual air/fuel ratio with respect to a target air/fuel ratio on a steady basis, and inhibits the purging operation performed by the evaporative fuel processing mechanism when a value representative of a variance of a first air/fuel ratio learned value corresponding to a highest engine load region among the plurality of engine load with respect to a second air/fuel ratio learned value corresponding to a lowest engine load region is equal to or larger than a predetermined value.
The rate of change in the quantity of the evaporative fuel in the lubricating oil is considerably lower than the rate of change in the fuel injection quantity resulting from the change in the engine operating state. The steady variance tendency of the actual air/fuel ratio with respect to the target air/fuel ratio according to the evaporative fuel quantity is reflected on the correction amount, i.e., air/fuel ratio learned value, for compensating the steady variance tendency of the actual air/fuel ratio with respect to the target air/fuel ratio.
During engine operation at low load, the quantity of the fuel injected from the fuel injection valve becomes relatively small. In this case, if the fuel evaporates from the lubricating oil, the ratio of the fuel evaporative quantity to the fuel quantity supplied to the internal combustion engine becomes higher compared with the engine operation at high load. That is, the air/fuel ratio variance tendency obtained during the engine operation at low load is different from the variance tendency obtained during the engine operation at high load.
In the aforementioned embodiment, performance of purging is inhibited if the variance of the air/fuel ratio learned value between the low load engine operation and the high load engine operation is determined to be larger than the predetermined value. This makes it possible to accurately determine that the quantity of the evaporative fuel from the lubricating oil is increasing. On the basis of the determination, performance of purging is inhibited.
The variance tendency may be derived from the deviation between the air/fuel ratio learned value KGH obtained during engine operation at high load and the air/fuel ratio learned value KGL obtained during engine operation at low load, that is, KGH-KGL or the ratio of the KGH to the KGL, that is, KGH/KGL. In the case where no fuel evaporates from the lubricating oil, it is effective to correct the aforementioned deviation or ratio to eliminate the variance tendency inherent to the engine existing between the KGH and KHL.
In the aforementioned embodiment, the controller inhibits the purging operation when the value representative of the variance tendency is equal to or larger than the predetermined value, and an air/fuel ratio correction amount of an air/fuel ratio feedback control obtained in accordance with a variance tendency of an actual air/fuel ratio with respect to a target air/fuel ratio increases by a predetermined amount or more so as to compensate the actual air/fuel ratio to a fuel rich side with respect to the target air/fuel ratio.
According to the embodiment, performance of purging is inhibited if the evaporative fuel quantity increases owing to the dilution of the lubricating oil and the variance of the actual air/fuel ratio with respect to the target values is caused by the increased evaporative fuel quantity. This makes it possible to avoid unnecessary inhibition of purging.
The error in learning of the purge concentration becomes noticeable particularly when the fuel injection quantity from the fuel injection valve becomes relatively small. Therefore, in the embodiment, the controller inhibits the purging operation when the engine is operated in a low load state.
According to the embodiment, performance of purging is inhibited during the engine operation at low load. Accordingly, the error in learning of the purge concentration may be prevented in the engine operation at low load while avoiding unnecessary inhibition of purging in the engine operation at high load.